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Why build piers in obs instead of just using a tripod?

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#1 nathmath

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Posted 24 December 2020 - 09:23 AM

I'm curious why so many people build big permanent piers in their observatories instead of just using a tripod on a cement slab? On one hand, I get it... a big pier is going to be super stable long term. And with a pier it's easy to reach zenith with long refractor setups. But I don't see how a quality tripod/tripier on a cement slab that allows zenith views is any worse. And you get the benefit of it being easily moveable if you wish.

#2 junomike

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Posted 24 December 2020 - 09:34 AM

IMO Stability (as you mentioned) is probably the most obvious. 

Also, mobility is the least of consideratioin

Finally, a Pier offer more room as the spread of the Tripod legs can take up valuable real estate.


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#3 wrvond

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Posted 24 December 2020 - 09:35 AM

Actually, what they are doing is building an observatory around their pier.

The benefits of a pier are obvious, so once an astronomer has decided to commit to pier mounting their scope(s), the next issue is protecting those scopes and mounts from the elements. Hence the observatory.


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#4 WadeH237

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Posted 24 December 2020 - 09:39 AM

I'm currently in the planning stages of my observatory, and am using my portable field pier for the time being.

 

The issue with the portable pier, or a tripod, is that over time, there is always some settling.  Most of the year, this is not a huge problem, but in the winter time, the cycles of freeze and thaw move the pier a surprising amount.  Installing a permanent pier would get the footing below the frost line, where the ground is much more stable.

 

So sure, you could just build a roll-off roof shed with a hole in the floor to put the tripod on the ground.  It would work fine for the short term, but a properly anchored pier will be much more stable.  I fully agree with the statement above that people are building observatories around the pier.


Edited by WadeH237, 24 December 2020 - 09:40 AM.


#5 D_talley

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Posted 24 December 2020 - 09:41 AM

A pier is isolated from the floor of the observatory normally.  Not so for a tripod on a cement slab.  



#6 gnowellsct

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Posted 24 December 2020 - 09:48 AM

The setup of a pier if it is well executed is to have the pier set in its own concrete with a opening in the cement floor for the pier to pass through which is completely independent of the cement floor. So no matter how many people go in there and how much they jump up and down they will be no transmission of the vibration to the instruments.

A secondary consideration is that a permanently mounted pier may provide some protection against theft as it is a daunting task to disassemble something like that for the uninitiated. But if you're in an observatory with theft on your mind you probably know what it is you're stealing.

Another factor is set up time. You might think if you leave the tripod that the setup time with a pier will be identical but the tripod is subject over time to small movements. these small movements can contribute to detectable pointing and tracking inaccuracies especially for long exposures. On a good tripod or p i e r it very much is possible to get your tripod dialed in to provide highly accurate pointing and tracking. But you may find yourself needing to check it more often than if you have a pier. We have pointing and tracking systems today which work to within a few arcseconds of tolerance and the tripod just introduces the possibility of errors due to getting kicked or jostled.

As a final point the people who install observatories with imaging equipment and a paramount or astrophysics German equatorial are often spending north of $50,000. For these people saving one or $2,000 on a new or used portable pier like the ATS, for the purpose of going to star parties, it's not such a big deal.

Indeed such people may have a $15,000 paramount on a pier in an observatory and when they go to a star party may take a Losmandy g11 on a tripod which they keep around for just that purpose. And they may have C11 or C8 which serves as their portable scope so they don't have to move that $25,000 apo.

The idea of having a complete second observing system including mount and telescope may strike some members as an eye-popping expenditure. And indeed it is. But if you spend $2,000 a year on this hobby which is not huge in the scheme of things after 20 years you're going to have some pretty cool stuff and a lot of different options.

I remember complaining to Marvin at company seven that I thought it was a hassle to put 2 inch adapters into the telescope and then take it out again when I wanted to use a 2-inch eyepiece. He said oh well I just put a 1.25 to 2 inch adapter on all my 1.25 inch eyepieces and leave them there. This idea was so novel and the notion that one would have 10 individual $30 adapters for 10 individual eyepieces struck me as an astounding indulgence.

But it's the system that I adopted two or three years later and the 300 bucks I dropped to get those adapters seems pretty trivial relative to the eye pieces that go into them.

So the answer to your question resides in some aspects of technical performance and some aspects of disposable income and yet again within the context of given levels of income different priorities. one guy has three kids in college and another guy does not. And these are the things that go into the decision as to whether to get a permanent pier or a tripod... or both.

Edited by gnowellsct, 24 December 2020 - 09:54 AM.


#7 c2m2t

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Posted 24 December 2020 - 10:03 AM

Hi Nathmath!

If you have been at the hobby a while, you grow tired of kicking tripod legs frown.gif grin.gif . Tripods can work but there is a far greater chance for vibrations to be transmitted to the mount and scope. For any serious astronomy, a pier is really the best option...and it frees up floor space which is critical in a confined space...which most home observatories have.

 

Cheers, Chris.


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#8 mrlovt

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Posted 24 December 2020 - 10:32 AM

I have two large tripods set up in the observatory now, but they'll soon be replaced by piers.  That was always the plan, I just didn't get around to pouring them before winter.  Tripods eventually settle, and are more affected by the seasonal ground swell and shrinkage.  And as Chris said, eventually you get tired of kicking tripod legs.  Or, in my case, of doing the dance to move between the two scopes without hitting an OTA or a counterweight shaft.  sct.pngIhavenojoints.gif Telescope.gif

 

Now if I could just find room for one more...   It's a 10x10 ROR observatory, I could probably manage 3 piers, right?  lol.gif



#9 Astrola72

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Posted 24 December 2020 - 11:02 AM

Gremlins are attracted to tripods. Piers, not so much.


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#10 Sandy Swede

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Posted 24 December 2020 - 11:11 AM

Hmm.  In the tripod on a concrete slab scenario, if once polar aligned, would there be any day to day or week to week variations which could be detrimental to AP?  In other words, would you still have to check and possibly adjust your polar alignment?



#11 kathyastro

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Posted 24 December 2020 - 11:18 AM

And you get the benefit of it being easily moveable if you wish.

For most people, easily movable is not a benefit.  If I accidentally kick my pier, I may lose the current exposure.  If I accidentally kick a tripod, I lose my polar alignment.  My tripod is still easily movable.  It is just folded up in the corner.


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#12 slepage

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Posted 24 December 2020 - 11:29 AM

I'm not a big fan of concrete slabs in the observatory.  I live in an area were the summertime temps are in the 100's and the concrete absorbs all that heat and then takes much longer to reach ambient temp at night.  A real problem for doing high resolution planetary work.  So for me the only way is to build at permanent pier in the ground and have a raised wooded floor that does not touch the pier in anyway. 


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#13 mikenoname

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Posted 24 December 2020 - 10:07 PM

If you have been at the hobby a while, you grow tired of kicking tripod legs frown.gif grin.gif .

Testify. I have never tripped over my pier, but I swear those tripod legs reach out and grab you.


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#14 nitegeezer

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Posted 24 December 2020 - 10:26 PM

Testify. I have never tripped over my pier, but I swear those tripod legs reach out and grab you.


The whole reason I wanted to have my observatory was so my alignment was good to start. With a tripod I would never expect that.

I guess I should also add that my pier does not extend into the ground, instead it is a tire filled with 750 lbs of concrete. The tire keeps me from bumping the scope in the dark, and it is movable with a good size tractor. I experimented with it to find where I wanted my observatory and it is not close to where it started!!
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#15 nathmath

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Posted 25 December 2020 - 08:59 AM

Thanks for all the input everyone. I suppose I realized most of these points intuitively. In my case I don't have an observatory, but would like to build one sometime in the next few years so I'm thinking ahead. My use case would be AP and controlling everything remotely so I'm not worried about walking into the tripod or transmitting vibrations through the floor. Likewise, the smaller footprint of the pier would be a moot point if the area in space around the telescope has to remain clear for it to swing around. The mobility part seems nice if I ever need to rearrange different setups, perhaps to accommodate new scopes/mounts--of course I could just pour an extra pier or two in any ROR I build just to be safe.

 

I was also thinking about if I ever needed to move or leave the ROR behind... it might be easier to convince a future buyer that the ROR can easily be used as a shed if there aren't big concrete piers in the middle of it.

 

The settling point is most interesting as I live in the midwest with a large swing in temperatures with the seasons. I don't even know how much concrete would be necessary to pour a slab that would resist heaves from freeze-thaw cycles but I suppose it could be more than a pier set deep below frost line.


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#16 jcj380

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Posted 25 December 2020 - 09:12 AM

Hmm.  In the tripod on a concrete slab scenario, if once polar aligned, would there be any day to day or week to week variations which could be detrimental to AP?  In other words, would you still have to check and possibly adjust your polar alignment?

Concrete slabs can settle and crack.  How much and how fast is highly variable, according to a friend who does concrete work for a living.



#17 SeymoreStars

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Posted 25 December 2020 - 09:26 AM

DSC00990
Tripod - OK.
20180409 131146
Concrete pier with four feet deep footer - more better.
20180923 140930
Two concrete piers with four feet deep footers - much more better.
20181115 132038
Two concrete piers with unattached wooden deck - much, much more better.
20181119 070754
Remote controlled observatory with two concrete piers  - much, much, much more better

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#18 Jon Isaacs

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Posted 25 December 2020 - 10:25 AM

I think if you look at the best tripods, they look very much like a pier.

 

http://www.company7....nacle400512.jpg

 

Jon

 

 



#19 Alex McConahay

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Posted 25 December 2020 - 12:20 PM

>>>>>>>I was also thinking about if I ever needed to move or leave the ROR behind... it might be easier to convince a future buyer that the ROR can easily be used as a shed if there aren't big concrete piers in the middle of it.

 

Pour the concrete to below the floor, with anchor bolts sticking up. Then run steel pier to where it is needed. When you have to move, unbolt the pier, and cover the hole in the floor. 

 

I don't know how you explain the moving roof, though. 

 

Alex



#20 csandfort

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Posted 25 December 2020 - 12:44 PM

I don't know how you explain the moving roof, though. 

 

Alex

 

An ultra private place to sun your bum?


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#21 Gastrol

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Posted 26 December 2020 - 12:36 AM

Being in and out of the hobby several times since I built my obs I often wish I had just simply poured a deep, 4’ x 4’ square slab and built my 8’ x 10’ obs around it instead of the 12” diameter concrete pier.   The pier is completely isolated, offers more free space and leg room but using a tripod on a slab would have been fine for my visual only setup.

One day if I ever hang up this hobby for good it’ll be a b*tch to cut or demolish the rebared pier so I can turn the obs into a storage shed.



#22 mark77

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Posted 26 December 2020 - 10:41 AM

My pier has over 500 pounds of equipment sitting on top of it.  No way a tripod is going to support that.

 

PS. my system is NOT portable.....


Edited by mark77, 26 December 2020 - 10:41 AM.


#23 DeanS

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Posted 26 December 2020 - 11:25 AM

My scope room is about 11' x 11' inside.  I have 2 piers, and a tripod along the south wall set up with a small wide field scope.  Very tight arrangement but scopes do not interfere with each other at all.  The tripod/mount was really to be temporary, but that was about a year ago wink.gif

 

Observatory pad is very deep solid concrete and I get no vibrations from walking around carefully.  Tripod legs are a pain to deal with particularly when dark.  

 

Here is a monitor camera pic.

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  • obs2.PNG

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#24 DeanS

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Posted 26 December 2020 - 11:29 AM

>>>>>>>I was also thinking about if I ever needed to move or leave the ROR behind... it might be easier to convince a future buyer that the ROR can easily be used as a shed if there aren't big concrete piers in the middle of it.

 

Pour the concrete to below the floor, with anchor bolts sticking up. Then run steel pier to where it is needed. When you have to move, unbolt the pier, and cover the hole in the floor. 

 

I don't know how you explain the moving roof, though. 

 

Alex

The moving roof can be for shy people that want to sunbath in the nude ;)


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#25 SeymoreStars

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Posted 26 December 2020 - 12:06 PM

  Tripod legs are a pain to deal with particularly when dark.  

Tripod legs are great if you like to polar align regularly. I polar align once every two years.


Edited by SeymoreStars, 26 December 2020 - 12:07 PM.

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